In the manufacture of containers such as glass bottles and jars, various types of anomalies can occur in the sidewalls, heels, bottoms, shoulders, necks and/or finishes of the containers. These anomalies, termed “commercial variations” in the art, can affect commercial acceptability of the containers. It has been proposed to employ electro-optical inspection techniques for detecting commercial variations that affect the optical properties of the containers. The basic principle is that a light source is positioned to direct light energy onto the container, and a light sensor is positioned to receive an image of a portion of the container illuminated by the light source. U.S. Pat. Nos. 4,378,493, 4,610,542, 5,442,446 and 6,067,155 disclose inspection systems in which a light source and a light sensor are positioned on opposite sides of a container under inspection. Opaque and refractive commercial variations, in a portion of the container illuminated by the light source, are detected as a function of light intensity in an image of the illuminated portion of the container received at the sensor.
A problem is encountered when inspecting the sidewalls of containers, particularly large-diameter containers such as baby food jars and other food containers. The push-up on the container base, the curvature of the container shoulder and/or heel, and the container support mechanism on the back side of the container can affect the ability to inspect the entire container sidewall and result in false indications of commercial variations in the container sidewall. Inspection systems consequently typically inspect the central portion of the container sidewall, and leave the shoulder and heel portions uninspected. It is a general object of the present invention to provide an apparatus for inspecting container sidewalls in which the shoulder and/or heel portion of the container sidewall can be inspected without producing false indications of commercial variations.
Apparatus for inspecting containers having a container sidewall with a shoulder and a heel, in accordance with one aspect of a presently preferred embodiment of the invention, includes a device for positioning a container for inspection, a light source on one side of the container positioning device, and a camera having a light sensor and an entrance pupil on an opposing side of the container positioning device. A lens, preferably a fresnel lens, is disposed between the camera and the positioning device. The fresnel lens is positioned with respect to the entrance pupil of the camera so that the light sensor has a field of view that is directed by the fresnel lens through the container sidewall onto the light source at a first converging angle through the shoulder and at a second converging angle through the heel. The positioning device preferably is such that a front surface of the container is positioned adjacent to the fresnel lens, and such that the fresnel lens has a focal point disposed between the container front surface and the light source. The container positioning device may take any number of forms, but preferably is such as to hold the container in stationary position while rotating the container around an axis. The focal point of the fresnel lens preferably is disposed between the light source and the axis of container rotation.
Apparatus for inspecting a container sidewall having a shoulder and a heel, in accordance with a second aspect of the preferred embodiment of the invention, includes a device for positioning a container for inspection, a light source on one side of the container positioning device, and a camera having a light sensor with a field of view and an entrance pupil on an opposing side of the positioning device from the light source. A lens system is disposed between the camera and the positioning device such that an upper portion of the camera field of view is directed by the lens system, preferably a fresnel lens, at a downward angle through the container shoulder toward the light source, and a lower portion of the camera field of view is directed by the lens system at an upward angle through the container heel toward the light source. The lens system preferably directs the rays of the camera's line of sight through a field of view at the container wall being inspected to a convergence point at or near the light source.